A conventional pressure measurement cell has a ceramic base body that is essentially cylindrical at least in sections, a ceramic measuring membrane and a capacitive transducer, wherein the measuring membrane is joined to the base body in a pressure-tight manner along a circumferential joint and a measurement chamber is formed between the measuring membrane and the base body, wherein the measuring membrane is deflectable from a resting position of the measuring membrane into a pressure-dependent position as a function of a difference between a first pressure on an outer side of the measuring membrane facing away from the measurement chamber and a second pressure in the measurement chamber, wherein the capacitive transducer has a membrane electrode facing the base body, and wherein the base body has at least one first base-body electrode facing the measuring membrane, wherein the capacitance between the at least one membrane electrode and the first base-body electrode is a function of the pressure-dependent position of the measuring membrane.
For joining the two bodies, meaning the base body and the measuring membrane, so-called active solders are used, which typically melt between 600 and 1000° C. and are usually processed at 800 to 1050° C. By using active solders, direct welding of ceramics without additional metallization is possible. These solders are metallic solders that can, because of their alloy composition, wet non-metallic, inorganic materials. They normally contain components, such as titanium, zirconium or hafnium, that react with ceramics. Such active solders in the form of metallic foils can be manufactured using a melt spinning method, wherein only a minimum thickness of about 25 micrometers is achievable due to technical constraints. Subsequent processing to reduce the thickness of the metallic foil, for example, using a rolling method, is not possible.
When using active solders of this sort, meaning metallic foils, for joining the base body and the measuring membrane, the distance between the base body and the measuring membrane, which together form the measurement chamber, is determined by the thickness of the active solder. From a manufacturing standpoint, however, such metallic foils, as already mentioned, cannot be manufactured thinner than about 25 micrometers. Accordingly, pressure measurement cells known from prior art have a distance between the base body and the measuring membrane of at least about 25 micrometers.
With regard to the measurement performance of the pressure measurement cell, however, it is advantageous to have a substantially smaller distance because the distance substantially influences two parameters of the pressure measurement cell. First, the maximum allowable overpressure or the maximum overload that can be applied to the outer side of the measuring membrane facing away from the pressure chamber without the measuring membrane being destroyed; and second, the resolution of the measurement signal which increases with a smaller distance, since the pressure measurement cell works in a range of larger capacitance.
In general, the measuring membrane is deflected out of its resting position when pressure is applied to the outer side of the measuring membrane facing away from the pressure chamber. The measuring membrane is deformed or deflected in the direction of the base body in this case and is partially pressed onto the base body as a result of a corresponding pressure. After removal of the pressure, the measuring membrane again returns to its resting position.
In the event that the maximum overload is exceeded, meaning the application of a pressure above the maximum allowable overpressure, the measuring membrane is deflected so far that such huge tensile stresses are caused on the outer side facing away from the measurement chamber that the measuring membrane is or can be destroyed. This damage can be avoided if a distance between measuring membrane and base body is selected at which the measuring membrane largely rests against the base body before such huge tensile stresses arise so that further mechanical deformation is not possible.